XPS spectroscopic study of potentiostatic and galvanostatic oxidation of Pt electrodes in H2SO4 and HClO4

The surface oxides produced from potentiostatic and galvanostatic oxidation of Pt electrodes in HClO4 and H2SO4 are examined using X-ray photoelectron spectroscopy. The oxide I species produced as the initial oxidation product by successively more anodic potentiostatic oxidation in 0.2 M HClO4 is found to have a Pt2+ oxidation state, a binding energy characteristic of neither PtO, Pt(OH)2 or PtO2, and a limiting thickness of 8 Å. Galvanostatic oxidation in HClO4 and H2SO4 is found to produce PtO2·H2O as an unlimiting growth oxide or a limiting growth oxide layer depending on the concentration of the acid electrolyte. The incorporation of the acid electrolyte anion in the surface layer is shown to have an effect on which type of oxide layer is produced. X-ray decomposition and chemical modification by Ar+ stripping are shown to produce chemical artifacts complicating any interpretation of a Pt oxide surface layer.